The present invention relates to a process for the purification of crude 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane (= tetramethyl-bisphenol A= TMBPA) by recrystallization from aqueous solutions of alcohols.
In principle, it is known to recrystallize bisphenols from aqueous solutions of lower alcohols. DE-OS (German Published Specification) 2,758,565 describes for this purpose chiefly glycols or ethers thereof, and glycerol, phenol and ethanolamine as alcoholic solvents. which are to be used. These solvents however are recoverable only with difficulty and are not allowed to enter waste water due to their toxicity (for example toxicity to fish) but must be disposed of separately. The said DE-OS also specifies a solvent mixture comprising ethanol and water in the example of bisphenol A which is to be recrystallized. In this recrystallization, an amount of 500 g of water and 102 g of ethanol are used per 50 g of bisphenol A, in order to completely dissolve the bisphenol A at 100.degree. C. Thus more than 600 g of solvent in total are necessary per 50 g of the bisphenol A which is to be recrystallized. Obviously, the purification process of the above DE-OS is based on the notion that mainly a poor solvent with a high water content must be used in order to minimize crystallization losses.
However, TMBPA cannot be recrystallized under these conditions.